1. Field of the Invention
This invention relates to a self-contained air unit for installation on a roof top of a building, the unit having a pressure relief opening that is independent of the air circulation system of the unit, the air circulation system having a first blower, the pressure relief opening having a damper system that connects the pressure relief opening to ambient air through two passages, a first passage being through a fourth damper to ambient air and a second passage being through a third damper to a passage containing a second blower to exhaust air from the air circulation system and from the Independent pressure relief opening simultaneously.
This invention further relates to a two-stage pressure relief hood for use with a self-contained air unit for installation on a roof top of a building for circulating air through the building, the unit having an air circulation system with a first blower connected to circulate air into and out of the building with a pressure relief opening that is independent of the air circulation system. The pressure relief opening has two stages, the first stage being a first passage that connects the pressure relief opening to ambient air through a fourth damper, and a second stage, being a second passage that connects the independent relief opening through a third damper to a second blower that is connected to exhaust air from the building through the air circulation system and simultaneously to exhaust air from the building through the independent relief opening.
2. Description of the Prior Art
Self-contained air units for installation on a roof top of a building for circulating air through the building are known and prior units have a first blower that is connected to a circulation system in order to circulate air into and out of the building and to introduce fresh air and exhaust stale air from the building. It is also known to have an air unit with an independent relief opening as described in US Application Publication No. US2007-0190925.
Self-contained air units are manufactured with a particular size and a cross-sectional area of the independent pressure relief opening is limited in size and is sometimes too small compared to the size of the independent relief opening required for a particular building in order to ensure that there will be no build-up of pressure in the building beyond the pressure of ambient air.